Presented at OSU Graduate Seminar, April 1, 2013

Material Challenges and Opportunities for Commercial

Electric Aircraft

Dr. Ajay Misra NASA Glenn Research Center

Cleveland, OH Presented 38th International Conference on Advanced Ceramics and Composites Daytona Beach, FL , Jan 28, 2014

https://ntrs.nasa.gov/search.jsp?R=20140017337 2018-06-01T07:23:05+00:00Z

NASA Goals for Fixed Wing Aircraft

Benefits of Electric Propulsion

• Significantly reduced emission (near zero for certain concepts) – green system

• Significant reduction in fuel burn due to higher efficiency of electrical systems

• Reduction in noise

• Advanced concepts (such as distributed propulsion and boundary layer ingestion) might be enabled by certain electric propulsion concepts

Possible Future Commercial Large Transport Aircraft

FAN

MOTOR

ELECTRIC BUS (TRANSMISSION

LINE) BATTERY

PACK

TURBINE ENGINE

FUEL

MOTOR

Hybrid Electric

TURBINEENGINE

GENERATOR MOTOR

FAN

ELECTRIC BUS (TRANSMISSION

LINE)

Turbo Electric

Both Concepts can use either non-cryogenic motors or cryogenic superconducting motors.

Non-Prop Power

Energy storage for power mgmt

N p

Non-Prop Power

Energy storage for power mgmt

ERA

n Pr p

All Electric Propulsion

FAN

MOTOR ELECTRIC

BUSS

(TRANSMISSION LINE)

MOTORBATTERY

PACK

FUEL CELL

FUEL

EADS – VoltAirs concept • Li-Air battery • High temperature superconducting motor

kW class

1-2 MW class

2-5 MW class

5-10 MW

• Turboelectric 50 PAX regional • Turboelectric distributed propulsion 100

PAX regional

• Turboelectric 100 PAX regional • Turboelectric distributed propulsion

150 PAX

• Hybrid electric 737-150 PAX • Turboelectric 737-150

PAX

> 10 MW

Pow

er L

evel

for E

lect

rical

Pro

puls

ion

Sys

tem

Today 10 Yr 20 Yr 30 Yr 40 Yr

• Turboelectric and hybrid electric distributed propulsion 300 PAX

• All electric and hybrid electric GA

Notional Timeline

Progression of Adoption of Electric Propulsion in Aircraft

Key Challenges for Large Commercial Electric Aircraft

High power density superconducting motor (cryogenic)

High power density non-cryogenic motor

Lightweight thermal management system

High power density power electronics

Lightweight power transmission cable

Energy storage system with high specific energy

Power Density of Gas Turbine Engines Compared to Projected Power Density of Electric Motors

5

10

15

20

25

30

10 15 20 25 30 5

Years From Today

Pow

er D

ensi

ty, h

p/lb

Gas Turbine Engine

Non-Cryogenic Motor

Superconducting (Cryogenic) Motor

Fully Superconducting Motors Needed for Electric Aircraft

MgB2 easy to fabricate in coil form – needs liquid hydrogen for cooling • The state-of-the-art

superconducting motor is limited to application of superconducting materials in rotor coils only

• Application of superconducting material in stator coils is limited by high ac losses due to the effect of varying magnetic field

The challenge for fully superconducting motor is to develop low ac-loss stator coils

Key Materials Challenge for Fully Superconducting Motor

MgB2

Nb (reaction barrier)

Cu

Cu-Ni sheath

Reduction of ac-loss in superconducting coil requires: • Reducing filament size (state-of-

the-art filament size on the order of 70-100 microns, experimental filaments of 30 micron diameter, need to reduce diameter to 10 microns or lower

• Twisting wire with reduction in twist pitch

• Increasing resistivity of sheath material and reaction barrier

Significant manufacturing challenge to develop 10 micron or less diameter MgB2 filament with superconducting properties and required mechanical properties for stator coil application

Material Advancements Needed for High Power Density Non-Cryogenic Electric Motor

Magnets with higher energy product

Higher electrical conductivity coil

Higher temperature magnets

Stator coil insulation material with high

thermal conductivity and higher temperature

capability

Coils With High Electrical Conductivity

Iodine-doped CNT from Rice University (2011)

2013- carbon nanotube fiber with high specific electrical conductivity by Rice Univ.

Challenge: • CNT fiber with electrical

conductivity greater than Cu • Fabrication of coils with CNT

fiber • Motor design with CNT fiber

Development of Advanced Magnets

Breakthrough needed to significantly increase maximum energy product of magnets

High Temperature Magnets

No major improvement in increasing temperature capability of magnets over the last decade

Challenge is to develop high temperature magnets with high maximum energy product (BH) and temperature capability greater than 400oC required

Advanced Stator Coil Insulation Material

SOA polymer

Improved polymer

Polymer composite with conductive fillers

Challenge: • Polymer composite stator coil

insulation materials with order of magnitude increase in thermal conductivity

• Temperature capability of 400oC or higher

Power Electronics Semiconductor

Si ~ 150oC

SOA SiC ~ 250oC

SiC theoretical ~ 600oC

~ 15 mm Long Crystal

[1120]

[1100] 000

[0001]

Increase in power density by increasing temperature capability of semiconductor

Need temperature capability beyond the current state-of-the-art (SOAA)

High temperature packaging is a major barrier

Defect-free SiC for large wafers is a technical challenge

Capacitors for Power Electronics

From AFRL

Capacitors with higher energy density and higher temperature capability are required for increasing power density of power electronics

Advanced Capacitors for High Power Density Power Electronics

Ceramic capacitors with temperature capability beyond 200oC, but have low breakdown strength

Challenge: • Polymer-nanoceramic

composite with energy storage capability greater than 20 J/cm3

• High temperature ceramic capacitors with high breakdown strength

Polymer-ceramic nanodielectric

Material Advances Critical for Increasing Power Density of Power Electronics

1980 1990 2000 2010 2020

Year

100

10

1

0.1

0.01

Pow

er D

ensi

ty, k

W/L

Projected power density improvements for power electronics

Materials advances (higher temperature SiC semiconductor, high temperature packaging, and higher temperature capacitor with high energy density) are critical for 10-fold increase in power density of power electronics

Higher temperature and compact power electronics will enable placement of power electronics on motor

Lightweight Power Transmission • Electrical cables contribute to significant weight in commercial aircraft

– 140 miles of Cu electrical wiring in Boeing 747 contributing to 3500 lb of wiring • Transfer of MW of power in turboelectric and hybrid electric aircraft will require

significantly large diameter of Cu cables, adding significant weight • Lightweight power transmission system required

Superconducting transmission lines between generators and motors

Iodine-doped CNT from Rice University (2011)

High electrical conductivity carbon nanotube (CNT)

High voltage transmission

Higher temperature electrical insulation with high thermal conductivity (enables more current to pass through wire, allowing for use of fewer wire)

Material Challenges with Higher Voltage Power Transmission

Corona discharge problem at high voltage

Require materials with high relative permittivity and high breakdown voltage

High Energy Density Batteries Require Significant Advances in Materials

0

200

400

600

800

1000

1200

1400

Li-ion Li-S Li-Air

15 yr

15 yr

15 yr

30 yr

30 yr

30 yr

Requirements for hybrid electric aircraft

Ener

gy D

ensi

ty, w

att-h

r/kg

Dendrite growth on Li anode

Engineered porous cathode structure

IBM

Thermal Management Challenge

• 10 MW power system with 1% loss = 100 kW of heat to be rejected; 3 % loss = 300 kW of heat to be rejected

• Thermal management of each component – motors, power electronics, power transmission

• Integrated thermal management strategy required

• Lightweight thermal management system required

Graphite foam heat exchanger

Lightweight recuperator materials for cryocooler

Aligned nanotube as thermal interface material

Flexible and mechanically strong aerogel insulation

Material advances critical for lightweight thermal management system

Multifunctional Structures Enabling for Reducing Weight of Commercial Electric Aircraft

Batteries incorporated inside structure

Multifunctional battery with load-bearing capability

Conformal thin film battery

Multifunctional structure with load-bearing and thermal management capability

Summary Material advances critical for future large commercial electric aircraft: • Materials with electrical conductivity

higher than that of Cu • High temperature electrical insulation

materials with high relative permittivity and high breakdown voltage strength

• Magnets with high maximum energy product (BH)max

• Higher temperature magnets • Higher temperature power electronics

semiconductor and packaging technology

• Materials to enable orders of magnitude increase in energy density and power density of energy storage system

• Lightweight thermal management materials

• Multifunctional materials

• 5X increase in power density of electrical motors

• 10X increase in power density of power electronics

• 10X reduction in weight of power transmission

• 10X reduction in weight of thermal management system